The present invention relates to carbon nanotube-based multi-sensors, and more particularly, combined high sensitivity strain, temperature and/or humidity multi-sensors based on carbon nanotubes for microelectronic applications.
A chip typically includes integrated circuits formed by front-end-of-line (FEOL) processing and metallization levels of an interconnect structure formed by back-end-of line (BEOL) processing. The chips are packaged in modules and usually not directly mounted on a circuit board. Module packaging provides electrical connectivity between the chip and the circuit board, protection against thermal and mechanical stresses, and protection against environmental corrosion. Solder bumps are commonly utilized to provide mechanical and electrical connections between the last or top metallization level in the chip and the circuit board.
By way of example, C4 (Controlled-Collapse Chip Connection) can be utilized to connect integrated circuit chips to substrates in electronic packages. In particular, C4 is a flip-chip packaging technology in which the interconnections are small solder balls (or bumps or pillars) formed on the chip surface. The top layers of an integrated circuit chip include various wiring levels, separated by insulating layers of dielectric material, that provide input/output (I/O) for the device. In C4 structures, the chip wiring is terminated by a plurality of metal films that form the ball-limiting metallurgy (BLM). The BLM defines the size of the solder bump after reflow, and provides a surface that is wettable by the solder and that reacts with the solder material to provide good adhesion with acceptable reliability under mechanical and thermal stress. In addition, the BLM also serves as a diffusion barrier between the integrated circuit device and the metals in the interconnection.
Well established technologies like silicon-based piezo resistive or foil based as strain sensors, aluminum oxide-based or polyimide-based as humidity sensors, and transistors or diodes as temperature sensors are commonly used. However, disadvantages like size, low sensitivity, lack of positioning flexibility and/or incompatibility with existing micro-electronic processes limit their use especially for in-situ measurements in micro-electronic modules.